Particularly in the field of telecommunications, it is desirable to have an alternate, or "standby," power source if a primary power source is lost or becomes unreliable. Typical telecommunications facilities rely on commercial utilities as a primary source of power. A standby power source may take the form of, for example, a flywheel or an electrical generator driven by a fuel-powered engine.
Many types of standby power sources are available, including turbines, micro-turbines, rotary engines, and internal combustion engines. The selection of a particular type of standby power source requires consideration of not only the load requirements, but the available space to house the device and the maintenance requirements; unfortunately, in most applications, a compromise is required in an attempt to select a system having the best possible overall features and advantages. For example, many low-speed, high-torque devices are available that are governed to 3600 r.p.m., which can be used to generate a 60 Hz output. A low operating speed, however, translates into high-torque, which results in a large motor size. Because it is typically desired to house standby systems in very small areas, such as a cellular antenna facility, a large motor size is at the least undesirable, and possibly impracticable. Moreover, low-speed devices also typically require periodic maintenance. The foregoing disadvantages assoicated with the use of low-speed devices is, this, driving the trend in standby power systems toward the use of high-speed devices.
In recent years, many advanced, high-speed electrical generators or flywheels have been developed. The use of these newer high-speed devices is desirable because they are smaller in size than comparably rated low-speed devices, they are generally expensive, and they are typically low-maintenance. A design disadvantage of smaller size and higher r.p.m., however, is the difficulty or impracticability of designing a device capability of directly outputting 60 Hz power.
Conventional telecommunications systems are designed to operate from a source of 60 Hertz alternating current ("AC"), such as that provided by commercial utility systems; such systems also typically require a relatively stable input voltage. Modern, high-speed electrical generators and flywheels, however, typically provide raw output voltages that are both variable and at relatively high frequencies (e.g., 500 to 3000 Hz). Thus, conventional telecommunications system installations employing advanced, low-maintenance electrical generators or flywheels as a standby power source have required the use of a power conditioner. A power conditioner is a device that accepts a raw AC input voltage and provides a well-regulated output. If the raw output voltage of the standby power source is not at the desired operating voltage, the power conditioner must provide AC to AC voltage conversion; if the frequency of the raw output voltage is not at the nominal frequency of the primary source of power, e.g., 60 Hz, the power conditioner must additionally provide frequency conversion.
Conventional telecommunications system installations having a standby power source also employ a transfer switch; when the primary, or commercial, power source is lost, the transfer switch is used to disconnect the commercial power source and thereafter to connect the standby power source to the load. The transfer switch conventionally provides an open, or break-before-make, transition between the two power sources. More specifically, the transfer switch disconnects the initial commercial power source before connecting the alternate power source to the load. The open transition switching avoids any potential surges that may occur as a result of the two unsynchronized sources applying power to the load simultaneously.
The use of power conditioners and transfer switches in conventional standby power systems has several disadvantages. First, both devices are subject to failure, which may result, for example, in the loss of services provided by the telecommunications systems receiving power from a standby power system. Second, both devices may require periodic maintenance, which increases the cost of providing telecommunications services. Third, the cost of installing a standby power system is much greater than if the use of power conditioners and/or transfer switches were not required. Fourth, space is often limited in many applications, thus weighing against the use of or need for a power conditioner and/or a transfer switch.
Accordingly, what is needed in the art is a standby power system, and method of operation thereof, that provides more reliable operation, and reduced costs of installation and maintenance. Additionally, there is a need in the art for a telecommunications installation employing a high-rotational-speed (e.g. , greater thatn 3600 r.p.m.)standby power system that does not require the use of a power conditioner and/or a transfer switch.